In recent years, as energy saving, environmental protection, etc. have come to be considered more important, the requirement for lower fuel consumption of automobiles has become increasingly severe. In this connection, tires for automobiles are required to have a smaller rolling resistance so as to be able to contribute to lower fuel consumption. In order to allow a tire to have a smaller rolling resistance, there is generally used a rubber material for tire which can give a vulcanized rubber of higher resilience.
It has heretofore been proposed to obtain a high resilience by using, as a rubber material for tire, a rubber composition comprising a diene rubber and, as a reinforcing agent, silica in place of carbon black. This silica-containing diene rubber composition, however, has had a problem in that the composition is unable to give sufficient abrasion resistance and tensile strength as compared with carbon black-containing diene rubber compositions. One reason therefor is thought to be that the affinity of silica to diene rubber is smaller than the affinity of carbon black to diene rubber, making it impossible to obtain sufficient reinforcing effects.
In order to enhance the affinity of silica to diene rubber, it has been studied to use a diene rubber into which a group having affinity to silica is introduced. For example, in the case of diene rubber produced by emulsion polymerization, there was proposed a diene rubber into which a tertiary amino group is introduced (JP-A-1-101344); and in the case of diene rubber produced by anionic polymerization, there was proposed a diene rubber into which an alkylsilyl group (JP-A-1-188501), a halogenated silyl group (JP-A-5-230286) or a substituted amino group (JP-A-64-22940) is introduced.
Many of these diene rubbers into which one of the above-mentioned groups is introduced, however, strongly adhere to silica in blending with silica, causing insufficient dispersion; therefore, the resulting blends are inferior in processability and hardness property and are not sufficiently improved in properties such as resilience, tensile strength, abrasion resistance and the like.